A printed circuit board serves as a support chassis for the various electronic integrated circuits, resistors, capacitors, and other discrete components. The printed circuit board also provides the copper or other metallic conductors for conducting the electrical current between the various connecting terminals of the components. Printed circuit boards are usually preferred for the construction of any electronic circuit because they are easy and economical to mass manufacture, problems are easier to detect due to the orderly and observable conductor paths between terminals as compared to the maze of free wires present in other types of circuits, spurious problems occur less frequently because the conductors are fixed to the board, and the circuit is more compact.
The production of a printed circuit board upon which to assemble and test the electronic components of a prototype of a piece of electronic equipment is one of the critical steps in the successful development of the eletronic equipment. While techniques such as bread-boarding and wire-wrapping can be used in the early stages of the prototype testing, it is prudent practice to test final prototypes using a printed circuit board which duplicates the production product. A printed circuit board can create electronic anomalies which are not present in the bread-boarded or wire-wrapped prototype, or the printed circuit board can avoid problems which the bread-boarded or wire-wrapped prototype created. Thus, before mass production, the final production version of the printed circuit board must usually be derived. In practice, a series of prototype printed circuit boards usually evolve before a satisfactory final version is obtained. Adequate prototype testing can usually eliminate the necessity to make modifications in the printed circuit board after mass production of the electronic equipment commences.
In the past, one of the most significant problems in testing electrical prototypes using printed circuit boards was the time and expense required to produce the prototype printed circuit board. The usual process of producing a printed circuit board had to be followed regardless of whether a single prototype printed circuit board was required or whether a large number of mass produced printed circuit boards was required.
The most common process for producing printed circuit boards usually starts with making drawings of the printed circuit conductor pattern. The drawings can be manually prepared at great time and expense, or the drawings can be produced more economically and quickly with a computer containing printed circuit board computer aided design software and with a plotter controlled by the computer. A working copy or photographic positive is photographically produced from the drawings. Alternatively, a computer controlled photoplotter can be employed to directly create the working copy on a photographically treated plate. A copper clad board is next completely coated with photoresist material and allowed to cure. The working copy is placed over the cured photoresist material, and the photoresist material not shielded by the working copy is exposed. The photoresist material is developed and washed away, leaving the remaining photoresist material adhering to the copper surface in the printed circuit conductor pattern. The exposed copper is etched away in an etchant or acid bath to leave only the desired circuit pattern of copper on the plastic substrate of the board. The resist material resists the acid etchant effects and prevents the acid from etching away the thin layer of copper beneath the resist material, thereby leaving the conductors. After etching, the resist material is removed. Holes are drilled in the board at selected locations to receive the wire connection terminals of the electronic components to be soldered or attached to the printed circuit board.
The completion time for these conventional prior production processes may range from approximately one to eight weeks, with the typical average ranging between two and three weeks. Even when the process is accelerated as much as possible, significant time delays are common. One source of delay involves the photographic steps necessary to obtain the working master from the drawing and the photographic preparation of the circuit board prior to etching. Another practical source of delay is the fact that most printed circuit production facilities operate primarily for mass production purposes and have extensive backlogs for production. The typical cost of a commercially-produced single prototype printed circuit board of approximately six inches by eight inches with circuit conductors formed on both sides of the board can range from five hundred to one thousand dollars.
Other less common circuit board production techniques involve plating metal onto the copper or conductor pattern on the circuit board, or a catalytic technique which involves the electroless deposition of conductive conductors on a fiberglass substrate. These circuit board production methods involve intricate or time consuming steps and are also accompanied by various inconveniences.
It is apparent, therefore, that the various disadvantages of conventional circuit board production techniques hamper the individual production of single circuit boards. These disadvantages can seriously hamper the development, testing and prototyping of electronic equipment. The costs of producing printed circuit boards can also be prohibitive, especially when it is necessary to evolve a series of prototype printed circuit boards before the final desired version is achieved.